Thin film filters using omnidirectional reflectors

Abstract

An electromagnetic wavelength filter that allows the transmission of electromagnetic energy within a narrow range of wavelengths while reflecting incident electromagnetic energy at other wavelengths. The filter includes at least one cavity region; and at least two reflectors surrounding the at least one cavity region, at least one of the reflectors being an omni-directional reflector. The omni-directional reflector includes a structure with a surface and an index of refraction variation perpendicular to the surface, and the omni-directional reflector is specifically configured to exhibit high omni-directional reflection for a predetermined range of frequencies of incident electromagnetic energy for any angle of incidence and any polarization.

What is claimed is:  
     
       1. An electromagnetic wavelength filter that allows the transmission of electromagnetic energy within a narrow range of wavelengths while reflecting incident electromagnetic energy at other wavelengths, said filter comprising: 
       at least one cavity region; and  
       at least two reflectors surrounding said at least one cavity region, at least one of said reflectors being an omni-directional reflector, wherein  
       said omni-directional reflector comprises a structure with a surface and an index of refraction variation perpendicular to the surface, and said omni-directional reflector being specifically configured to exhibit high omni-directional reflection for a predetermined range of frequencies of incident electromagnetic energy for any angle of incidence and any polarization except at a predefined angle where electromagnetic energy of said narrow range of wavelengths is completely transmitted for all polarization states.  
     
     
       2. The filter of  claim 1 , wherein said narrow range of wavelengths is tuned by varying the incidence angle of the electromagnetic energy. 
     
     
       3. The filter of  claim 2 , wherein said incidence angle can be varied from 0 to 90 degrees of incidence. 
     
     
       4. The filter of  claim 1 , wherein said narrow range of wavelengths is tuned by thermal or electrical effects. 
     
     
       5. The filter of  claim 1 , wherein at a particular wavelength, said filter allows the transmission of electromagnetic energy at a single incident angle, or a small set of angles, while reflecting incident electromagnetic energy at all other incident angles. 
     
     
       6. The filter of  claim 5 , wherein said at least one narrow range of wavelengths overlaps for the TE and the TM polarizations. 
     
     
       7. The filter of  claim 5 , wherein said at least one narrow range of wavelengths exhibits similar width for the TE and the TM polarizations. 
     
     
       8. The filter of  claim 5 , wherein said at least one narrow range of wavelengths are different for the TE and the TM polarizations when said incidence angle is away from normal. 
     
     
       9. The filter of  claim 1 , wherein at an incident angle said filter allows the transmission of electromagnetic energy within at lease one narrow range of wavelengths while reflecting incident electromagnetic energy at other wavelengths. 
     
     
       10. The filter of  claim 1 , wherein said at least two reflectors comprise distributed Bragg reflector layers in the form of pairs of materials with different indices of refraction, said materials being semiconductors, conductive material oxides, glasses and glass-like oxides. 
     
     
       11. The filter of  claim 1 , wherein said filter comprises a single cavity. 
     
     
       12. The filter of  claim 11 , wherein said filter exhibits a Lorentzian transmission lineshape. 
     
     
       13. The filter of  claim 1 , wherein said filter comprises a plurality of cavities. 
     
     
       14. The filter of  claim 13 , wherein said filter exhibits a non-Lorentzian transmission lineshape. 
     
     
       15. The filter of  claim 1 , wherein said filter consists of materials with large index contrast. 
     
     
       16. The filter of  claim 15 , wherein said reflectors requires a defined number of layers to achieve a given narrow bandwidth. 
     
     
       17. The filter of  claim 15 , wherein said filter requires a defined number of layers to achieve a non-Lorentzian transmission line shape. 
     
     
       18. The filter of  claim 15 , wherein said filter comprises layers of Si and SiO 2 . 
     
     
       19. A wavelength division multiplexing filter that allows the transmission of electromagnetic energy within a narrow range of wavelengths while reflecting incident electromagnetic energy at other wavelengths, said filter comprising: 
       a filter, including at least one cavity region, and at least two reflectors surrounding said at least one cavity region, at least one of said reflectors being an omni-directional reflector, said omni-directional reflector comprising a structure with a surface and an index of refraction variation perpendicular to the surface, said omni-directional reflector being specifically configured to exhibit high omni-directional reflection for a predetermined range of frequencies of incident electromagnetic energy for any angle of incidence and any polarization except at an angle where electromagnetic energy of said narrow range of wavelengths is completely transmitted for all polarization states;  
       an input port;  
       an output port;  
       an add port; and  
       a drop port.  
     
     
       20. A method of filtering electromagnetic wavelengths that allows the transmission of electromagnetic energy within a narrow range of wavelengths while reflecting incident electromagnetic energy at other wavelengths, said method comprising: 
       providing at least one cavity region; and  
       providing at least two reflectors surrounding said at least one cavity region, at least one of said reflectors being an omni-directional reflector, wherein  
       said omni-directional reflector comprises a structure with a surface and an index of refraction variation perpendicular to the surface, and said omni-directional reflector being specifically configured to exhibit high omni-directional reflection for a predetermined range of frequencies of incident electromagnetic energy for any angle of incidence and any polarization except at an angle where electromagnetic energy of said narrow range of wavelengths is completely transmitted for all polarization states.